The purpose of this research is to investigate the biochemical characteristics of developing central nervous system (CNS) cells in culture, as discussed in previous reports. We have undertaken two approaches to this study: 1) We have designed a series of biochemical assays to distinguish various types of neuronal and non-neuronal cells in cultures from spinal cord and cerebral cortex of fetal animals, and, 2) we have employed these assays to assess the effects of chronic treatment of the cultures with neuroactive toxins and drugs, including anticonvulsants. The data collected thus far show that clinically-relevant doses of phenytoin and phenobarbital have toxic effects on developing neurons in culture. The effects of the two drugs on different cell types appear to be different. In addition, tetrodotoxin, which blocks neuronal sodium channels, appears to be selectively toxic for CNS neurons, but spares dorsal root gangion neurons.